Enhanced Audio Decoder

1. A method of decoding an audio signal, the method comprising: receiving, in an audio decoder, core audio data associated with a core portion of an audio signal and extension data associated with an extended portion of the audio signal; decoding the core audio data to generate a decoded core audio signal in a time domain representation; generating a reconstructed extended portion of the audio signal in accordance with the extension data and the decoded core audio signal in the frequency domain; filtering, using a highpass filter, the reconstructed extended portion of the audio signal to generate a reconstructed output signal; transforming, using a filter bank, the reconstructed extended portion of the audio signal into a time domain representation; and combining the decoded core audio signal and the reconstructed output signal to generate a decoded output signal after the reconstructed extended portion of the audio signal is transformed into a time domain representation.

2. The method of claim 1 , wherein the filter bank comprises a complex Quadrature Mirror Filter bank.

3. The method of claim 1 , wherein the extension data comprises spectral band replication data.

4. The method of claim 1 , further comprising: filtering, using a lowpass filter, the decoded core audio signal prior to the combining.

5. The method of claim 4 , further comprising: configuring the highpass filter and the lowpass filter to have a combined spectral response that equals a flat frequency response.

6. A computer program product, encoded on a non-transitory computer-readable medium, operable to cause data processing apparatus to perform operations comprising: receiving, in an audio decoder, core audio data associated with a core portion of an audio signal and extension data associated with an extended portion of the audio signal; decoding the core audio data to generate a decoded core audio signal in a time domain representation; generating a reconstructed extended portion of the audio signal in accordance with the extension data and the decoded core audio signal; filtering, using a highpass filter, the reconstructed extended portion of the audio signal to generate a reconstructed output signal; transforming, using a filter bank, the reconstructed extended portion of the audio signal into a time domain representation; and combining the decoded core audio signal and the reconstructed output signal to generate a decoded output signal after the reconstructed extended portion of the audio signal is transformed into a time domain representation.

7. The computer program product of claim 6 , further operable to cause data processing apparatus to perform operations comprising: filtering, using a lowpass filter, the decoded core audio signal prior to the combining.

8. The computer program product of claim 7 , further operable to cause data processing apparatus to perform operations comprising: configuring the highpass filter and the lowpass filter to have a combined spectral response that equals a flat frequency response.

9. The computer program product of claim 6 , further operable to cause data processing apparatus to perform operations comprising: generating subband signals based on at least a portion of the decoded core audio signal; and selecting, in accordance with the extension data, subband signals for use in generating the reconstructed extended portion.

10. A method of decoding an audio signal, the method comprising: decoding low frequency audio data corresponding to an audio signal portion below a cutoff frequency to generate a decoded low frequency signal having a time domain representation; generating high frequency audio data from extension data and at least a portion of the decoded low frequency signal; transforming, using a filter bank, the high frequency audio data into a time domain representation to generate a decoded high frequency signal; filtering at least one of the decoded low frequency signal and the decoded high frequency signal to reduce a distortion; and combining the decoded low frequency signal and the decoded high frequency signal to generate a decoded output signal.

11. The method of claim 10 , wherein generating high frequency audio data further comprises: generating subband signals based on at least a portion of the decoded low frequency signal; and selecting, in accordance with the extension data, subband signals for use in generating the high frequency audio data.

12. The method of claim 11 , further comprising: canceling the generated subband signals prior to transforming the high frequency audio data.

13. The method of claim 10 , wherein filtering further comprises: filtering the decoded low frequency signal using a lowpass filter that matches a response of the filter bank.

14. The method of claim 13 , wherein the filter bank comprises a Quadrature Mirror Filter bank.

15. The method of claim 10 , wherein filtering further comprises: filtering the decoded low frequency signal using a lowpass filter and the decoded high frequency signal using a highpass filter, wherein the lowpass filter and the highpass filter overlap for a portion of a frequency range of the audio signal.

16. A computer program product, encoded on a non-transitory computer-readable medium, operable to cause data processing apparatus to perform operations comprising: decoding low frequency audio data corresponding to an audio signal portion below a cutoff frequency to generate a decoded low frequency signal having a time domain representation; generating high frequency audio data from extension data and at least a portion of the decoded low frequency signal; transforming, using a filter bank, the high frequency audio data into a time domain representation to generate a decoded high frequency signal; filtering at least one of the decoded low frequency signal and the decoded high frequency signal to reduce a distortion; and combining the decoded low frequency signal and the decoded high frequency signal to generate a decoded output signal.

17. The computer program product of claim 16 , further operable to cause data processing apparatus to perform operations comprising: generating subband signals based on at least a portion of the decoded low frequency signal; and selecting, in accordance with the extension data, subband signals for use in generating the high frequency audio data.

18. The computer program product of claim 17 , further operable to cause data processing apparatus to perform operations comprising: canceling the generated subband signals prior to transforming the high frequency audio data.

19. The computer program product of claim 16 , further operable to cause data processing apparatus to perform operations comprising: filtering the decoded low frequency signal using a lowpass filter and the decoded high frequency signal using a highpass filter, wherein the lowpass filter and the highpass filter overlap for a portion of a frequency range of the audio signal.

20. A system comprising: an input configured to receive an audio bitstream; and an audio decoder including processor electronics configured to perform operations comprising: decoding low frequency audio data associated with the audio bitstream to generate a decoded low frequency signal, the low frequency audio data corresponding to an audio signal portion below a cutoff frequency; generating high frequency audio data from extension data associated with the audio bitstream and at least a portion of the decoded low frequency signal; transforming, using a filter bank, the high frequency audio data into a time domain representation to generate a decoded high frequency signal; filtering at least one of the decoded low frequency signal and the decoded high frequency signal to reduce a distortion; and combining the decoded low frequency signal and the decoded high frequency signal to generate a decoded output signal.

21. The system of claim 20 , wherein the audio decoder further comprises: a highpass filter and a lowpass filter configured to have a combined spectral response that equals a flat frequency response.

22. The system of claim 21 , wherein the highpass filter and the lowpass filter overlap for a portion of a frequency range.

23. The system of claim 20 , wherein the audio decoder further comprises: a delay element configured to delay the decoded low frequency signal.

24. The system of claim 23 , wherein a delay duration associated with the delay element corresponds to a processing delay of the filter bank.

25. The system of claim 20 , wherein the audio decoder further comprises: an analysis filter bank configured to generate subband signals based on at least a portion of the decoded low frequency signal; and a canceller configured to zero-out the generated subband signals.

26. The system of claim 20 , wherein the filter bank comprises a Quadrature Mirror Filter bank.